The invention relates to a method for the manufacture of a drawing die, in which a tube of a metal or a metal alloy is placed in a cavity in one side of a metal housing, a core is placed inside the tube, which has an internal diameter larger than the maximum dimension of the core, in a direction perpendicular to the axis of the tube, and the tube is deformed to reduce its axial dimension and its internal diameter to an extent such that an annulus is formed which grips the core and is a tight fit in the cavity of the metal housing, after which a drawing passage is provided in the core.
Drawing dies manufactured by such a method may be used, for example, for drawing wires.
A method as described above is known from U.S. Pat. No. 4,392,397, in which a strong temperature-resistant drawing die is obtained by clamping a metal annulus around the core by means of cold pressing. Unlike other known methods of manufacturing a drawing die (such as, embedding the core in bronze, or sintering or pressing into a metal powder) to bubbles and inclusions are formed. Moreover, the annulus subjects the core to an omnilaterial compressive stress which reduces the susceptibility of the core material to tearing.
However, this known method has a number of drawbacks which very much limit its practical use. Generally, the core will not remain level during the cold pressing of the annulus; it will e.g. tilt slightly which is impermissible in the case of a drawing die. Moreover, the annulus is deformed to such an extent that the upper side and the lower side of the core are partly covered with metal of the annulus. An additional treatment of the drawing die is necessary to clear the surfaces of the core. Furthermore, it has been found that the applicability of the method of this patent is limited if the core has a non-circular circumference.